This invention relates to a data communication control apparatus and method for implementing a multipoint videoconferencing system by controlling the communication of video and audio signals among a plurality of terminals. The invention relates also to a data communication system that includes this data communication control apparatus.
Multipoint videoconferencing systems that are currently proliferating make it possible for videoconferencing terminals in compliance with the standard of ITU-T Recommendation H.320 to communicate with one another from multiple locations.
ITU-T Recommendation H.231, which defines the functional framework of multipoint connection devices and the form of multipoint communications, and ITU-T Recommendation H.243, which establishes an in-channel communications procedure, have been set up as standards relating to multipoint connection equipment for controlling the connections at the multiple locations of videoconferencing terminals.
FIG. 6 is a block diagram illustrating the configuration of a multipoint videoconferencing system according to the prior art. The system includes a multipoint connection apparatus 122 compliant with H.231 and H.234, and videoconferencing terminals 121 compliant with H.320. The multipoint connection apparatus 122 interconnects the videoconferencing terminals 121 located at three or more points and supervises audio mixing, distribution of video data or multiple-screen synthesis of video data and chairperson control for facilitating conferencing. Thus, if the videoconferencing terminals are in compliance with H.320, a multipoint video conference connecting a plurality of remote locations can be realized by connecting the terminals via the multipoint connection apparatus.
However, an H.320-compliant videoconferencing terminal is very expensive because it is a dedicated terminal that necessitates high-load signal processing such as the compression and decompression of video data (ITU-T Recommendations H.261, H.263, etc.). Accordingly, it is difficult to realize a low-cost, low-power-consumption terminal that is capable of participating in videoconferencing, and to make such a terminal portable.
As a consequence of the foregoing, only a dedicated terminal can participate in conventional multipoint videoconferencing. In other words, a user can participate in conferencing only from a location at which a dedicated terminal has been installed.
In order to solve this problem, it has been proposed to provide the conventional multipoint connection apparatus not only with the function for interconnecting H.320-compliant videoconferencing terminals but also with a so-called voice gateway function that makes possible participation in a multipoint videoconferencing system by ordinary telephone.
FIG. 7 is a block diagram showing the configuration of a multipoint videoconferencing equipped with a telephone-based voice gateway function. As shown in FIG. 7, a plurality of dedicated videoconferencing terminals 131 and an ordinary telephone 133 are connected by a multipoint connection apparatus 132. In this system it is possible for the ordinary telephone 133 to participate in a multipoint video conference by voice only.
In a multipoint videoconferencing system of the kind illustrated in FIG. 7, it is possible to participate in a conference from an ordinary telephone but a sufficiently realistic sense of conference participation is not obtained merely by telephone-based voice. In addition, since participation in a conference from a telephone is limited to audio, naturally it is impossible to participate in data conferencing in accordance with ITU-T Recommendation T.120.